The development of reliable tools for assessing digital competences is of great importance. This is why we set out a re-evaluation of the measurement quality of the D21-Digital-Index assessment instrument. The D21-Digital-Index is a biannual and influential study held in Germany. The instrument used in the D21-surveys is based on the theoretical framework DigComp. In our analyses we used data of 1142 participants from vocational training and higher education institutions to estimate item parameters and the quality of the instrument using Item Response Theory. Because choosing an appropriate IRT-model is crucial for instrument evaluation, we calculated and compared two types of models, the Rasch and the Birnbaum model of which the latter turned out to achieve the better fit. In a unidimensional analysis the five scales of the instrument with 24 items in total yield acceptable measures. Multidimensional analysis shows a dimensional separation and hence confirms the construct validity of the instrument.

开发用于评估数字能力的可靠工具非常重要。这就是为什么我们重新评估D21数字索引评估仪器的测量质量的原因。D21数字索引是在德国进行的半年一次的有影响力的研究。D21调查中使用的仪器基于理论框架DigComp。在我们的分析中，我们使用了来自职业培训和高等教育机构的1142名参与者的数据，使用项目反应理论估算了项目参数和仪器的质量。由于选择合适的IRT模型对于仪器评估至关重要，因此我们计算并比较了两种模型，分别是Rasch模型和Birnbaum模型，后者证明它们能实现更好的拟合。在单维分析中，该仪器的五个量表（共计24个项目）可以接受。多维分析显示了尺寸分离，因此确认了仪器的构造有效性。